Use of Isolation STOPPLES® for Valve Replacement on Trans Alaska Pipeline

Abstract

In 1997 Alyeska Pipeline Service Company (Alyeska), operator of the Trans Alaska Pipeline System (TAPS), identified two mainline valves that required repair. The remote location, size and scale of these valves combined with the hydraulic profile of the pipeline presented significant challenges for the repair of the valves. Both valves were located such that the pipeline could not be simply drained to allow for repair or replacement. To drain the locations would have required facilities to drain, store, and re-inject or transport 108,000 bbls of oil. Isolation of these valves utilizing STOPPLES® reduced the volume of oil that needed to be handled but required repairs to be conducted by personnel working in a confined space behind the STOPPLES®. The conceptual repair plan for each of these valves was evaluated through a Peer Review/Risk Assessment to validate or revise the isolation and repair concepts. This process provided the communication and evaluation methods that were necessary to gain acceptance of the use of STOPPLES® for isolation by the organizations performing the work, state and federal agencies monitoring the work, and TAPS stakeholders. The work on Remote Gate Valve 80 (RGV 80) and Check Valve 122 (CKV 122) was completed during a single 28 hour pipeline shutdown in September of 1998. Both valves were isolated with STOPPLES® to minimize the crude handling requirements. This paper describes the repair of these valves from the conceptual design through the completion of the work.